Anisotropic exchange coupling interaction between hard–hard magnetic grains in sintered SrFe ₁₂O ₁₉ ferrites

The exchange coupling interaction in sintered magnetic materials is generally isotropic. In this study, an anisotropic exchange coupling interaction was found in the sintered oblate cylindrical SrFe₁₂O₁₉ specimens obtained by using SrFe₁₂O₁₉ nanopowders synthesized via a hydrothermal method. According to the Henkel plots, the exchange coupling interaction between hard-hard magnetic grains was found in both the as-pressed and the sintered specimens. However, the exchange coupling interaction can only be found in the in-plane but not in the out-of-plane direction for the sintered specimens. Through building a model of grain configuration, this anisotropy of exchange coupling interaction was ascribed to the vertically arranged plate-like SrFe₁₂O₁₉ grains with micrometers in width but nanometers in thickness, which was confirmed by the morphology of cross section in the fractured specimens.